Assad's rule coming to end, says Tillerson, as G7 rejects Johnson's call for more sanctions

Speaking at the G7 summit in Italy, Mr Tillerson said it was unclear whether Russia had failed to take seriously its obligation to rid Syria of chemical weapons or had merely been incompetent. But he noted that the distinction did “not much matter to the dead".

He went on: "We cannot let this happen again. We want to relieve the suffering of the Syrian people. Russia can be a part of that future and play an important role or Russia can maintain its alliance with this group, which we believe is not going to serve Russia's interests longer term."

Since the US launched air strikes against Assad's forces in retaliation for a chemical attack on civilians last week, Trump administration officials have offered mixed messages about whether Washington believes Assad definitely must surrender power and when.

Mr Tillerson said it was clear the US saw no role for Assad in Syria's future, given that he had lost legitimacy.

"It is clear to all of us that the reign of the Assad family is coming to an end," declared the Secretary of State. "But the question of how that ends and the transition itself could be very important in our view to the durability, the stability inside of a unified Syria. That's why we are not presupposing how that occurs.”

He said the ceasefire talks that Russia and Iran had help broker in the Kazakh capital, Astana, could generate momentum towards broader talks about a political transition but only if the Astana talks succeeded in creating a durable ceasefire.

The resulting political talks would then take place under the auspices of the United Nations process in Geneva.

But Mr Tillerson noted: "To date, Astana has not achieved much progress."

He spoke after a meeting of "like-minded" countries was hastily arranged on the sidelines of the G7 summit, days after the US for the first time launched air strikes against Assad's forces.

Mr Johnson had been pressing for an extension of international sanctions against military leaders involved in the chemical weapons strike in Syria. But this was rejected as G7 foreign ministers said that first there had to be an investigation into last week's attack before any new measures could be adopted.

The Foreign Secretary made clear the option of sanctions remained on the table but the outcome would come as a disappointment to him as he had hoped to strengthen Mr Tillerson’s hand as the US Secretary of State prepared to confront the Russians over their support for Syria.

Angelino Alfano, the Italian foreign minister, said there had been “no consensus” on the UK’s call for more sanctions and stressed that the G7 had to have a “dialogue with Russia”. He added: “We must not push Russia into a corner.”

Mr Johnson echoed Mr Tillerson, saying Moscow now faced a “big strategic choice”.

He told Sky News: “Do they want to stick with this guy who is poisoning his own people and poisoning the reputation of Russia or do they want to be part of the solution?"

The Foreign Secretary said a new resolution on Syria would be tabled at the UN Security Council and that there would be a "chemical weapons group" inspection into what happened.

"After that, if of course we can find people, whether they are Syrians or whether they are Russians associated with the Syrian military operation, it is wholly appropriate that they should face economic sanctions or sanctions of some other kind," he argued.

"That is something that had wide acceptance around the table last night, but you have got to do things in the proper legal way,” Mr Johnson added.

Earlier, Theresa May and Donald Trump agreed in a telephone call that there was now a "window of opportunity" to persuade Mr Putin that it was time for him to abandon his Syrian ally.

A key diplomatic focus since the chemical attack has been on increasing pressure on Russia, Assad's strongest ally, which has used its own military to keep the dictator in power.

The US and others have said that Russia bears responsibility for the deaths of civilians at the hands of Assad given Moscow's role in guaranteeing the 2013 deal in which he was supposed to have given up his chemical weapons arsenal.

On Monday, the White House raised the stakes significantly when a senior US official said Washington had made the preliminary conclusion that Russia had known in advance of Syria's chemical weapons attack. Yet the US had no proof of Moscow's involvement, the official admitted.

That accusation will hang over Mr Tillerson's visit to Moscow, where he plans to meet Sergey Lavrov, his Russian counterpart, and possibly Vladimir Putin.

The Kremlin declined to say whether the Russian President would meet Mr Tillerson in line with its usual practice of not announcing such meetings ahead of time.

Washington has sought to minimise expectations for the trip or the likelihood that the US will leave with any concessions from Russia regarding its support for Assad.

Instead, it is hoping to use the visit - the first by a Trump cabinet official to Russia - to convey its expectations to Moscow and then allow the Russians a period of time to respond.

Though intended to punish Assad for a chemical weapons attack, the US strikes last week served to refocus the world's attention on the bloody war in Syria, now in its seventh year.

At the meeting in the walled Tuscan city of Lucca, the G7 countries were joined by diplomats from Muslim-majority nations including Jordan, Qatar, Saudi Arabia, Turkey and the United Arab Emirates.

The inclusion of those countries is important because the US strategy for Syria involves enlisting help from Middle East nations to ensure security and stability in Syria after the Islamic State group is vanquished.